Salinity tolerance, Na+ exclusion and allele mining of HKT1;5 in Oryza sativa and O. glaberrima: many sources, many genes, one mechanism?

Abstract

BackgroundCultivated rice species (Oryza sativa L. and O. glaberrima Steud.) are generally considered among the crop species most sensitive to salt stress. A handful of lines are known to be tolerant, and a small number of these have been used extensively as donors in breeding programs. However, these donors use many of the same genes and physiological mechanisms to confer tolerance. Little information is available on the diversity of mechanisms used by these species to cope with salt stress, and there is a strong need to identify varieties displaying additional physiological and/or genetic mechanisms to confer higher tolerance.ResultsHere we present data on 103 accessions from O. sativa and 12 accessions from O. glaberrima, many of which are identified as salt tolerant for the first time, showing moderate to high tolerance of high salinity. The correlation of salinity-induced senescence (as judged by the Standard Evaluation System for Rice, or SES, score) with whole-plant and leaf blade Na+ concentrations was high across nearly all accessions, and was almost identical in both O. sativa and O. glaberrima. The association of leaf Na+ concentrations with cultivar-groups was very weak, but association with the OsHKT1;5 allele was generally strong. Seven major and three minor alleles of OsHKT1;5 were identified, and their comparisons with the leaf Na+ concentration showed that the Aromatic allele conferred the highest exclusion and the Japonica allele the least. A number of exceptions to this association with the Oryza HKT1;5 allele were identified; these probably indicate the existence of additional highly effective exclusion mechanisms. In addition, two landraces were identified, one from Thailand and the other from Senegal, that show high tissue tolerance.ConclusionsSignificant variation in salinity tolerance exists within both cultivated Oryza species, and this is the first report of significant tolerance in O. glaberrima. The majority of accessions display a strong quantitative relationship between tolerance and leaf blade Na+ concentration, and thus the major tolerance mechanisms found in these species are those contributing to limiting sodium uptake and accumulation in active leaves. However, there appears to be genetic variation for several mechanisms that affect leaf Na+ concentration, and rare cases of accessions displaying different mechanisms also occur. These mechanisms show great promise for improving salt tolerance in rice over that available from current donors.

Molecular characterization and function analysis of the rice OsDUF946 family

“…LEA proteins are mainly low-molecular-weight (10-30 kDa) proteins involved in protecting higher plants from damage caused by environmental stresses, especially drought or dehydration [42][43][44][45]. HKT transporters mediate Na C unloading from the xylem under salinity stress, which prevents Na C overaccumulation in leaves, thereby protecting photosynthetic organs [46][47][48][49]. It is, therefore, tempting to speculate that the overexpression of OsDUF946.4 might have resulted in upregulated expression of LEA protein-like and HKT-transporter-like genes in E. coli, which could have led to the enhanced tolerance to drought and salinity.…”

Introgression the <i>SalTol</i> QTL into the Elite Rice Variety of Russia by Marker-Assisted Selection<br>

“…The Na+ and K+ content in shoots and roots were measured using a capillary electrophoresis system (Capel-105M; Lumex, Russia) according to the method of Platten et al (2013).…”

“…Presently, a major QTL SalTol associated with the Na-K ratio in rice and seedlingstage salinity tolerance, are marked on chromosome 1 (Platten et al, 2013). Nevertheless, allelic variations of microsatellite loci associated with specific trait in related groups of genotypes do not always correlate with that trait in genotypes other origins (Senadheera et al, 2009;Mardani et al, 2014).…”

“…DNA marker analyses provide several significant advantages in comparison with analysis of morphological and physiological traits (Collard et al, 2008;Usatov et al, 2014a). Almost any gene or locus may be marked, suggesting the existence of a number of such specific markers (Hospital, 2009;Platten et al, 2013). In particular, DNA markers may be successfully used in breeding of rice with respect to its tolerance to salinity (Ashraf et al, 2012).…”

Screening for salinity tolerance of Oryza glaberrima Steud. seedlings

“…Awala et al (2010) reported that O. glaberrima CG14 appeared rather salt-sensitive but the obtained hybrids after crossing this line with the O. sativa WAB56-104 cultivar produced hybrids exhibiting a high level of salinity resistance. Platten et al (2013) quantified Na + accumulation in several salt-exposed lines of O. glaberrima and identified a specific gene (OgHKT1;5) which partly contribute to regulate Na + absorption and translocation.…”